Prosthesis with resilient ankle block

ABSTRACT

An ankle block prosthesis is provided having a lower foot plate and an upper ankle plate connected by a monolithic ankle block. The foot plate, ankle plate and ankle block are generally sized to fit within a surrounding cosmesis. The foot is configured such that during a walking or running stride the wearer experiences a smooth rollover or transition of compressive forces from a heel-strike position to a toe-off position so as to provide a natural feeling foot during walking or running activities.

RELATED APPLICATIONS

This application is a continuation of application U.S. Ser. No.08/515,557, filed Aug. 15, 1995, now U.S. Pat. No. 5,800,569, which wasa continuation-in-part of U.S. Ser. No. 08/692,340 filed Aug. 5, 1996,now U.S. Pat. No. 5,728,177, which was a file-wrapper continuation ofU.S. Ser. No. 08/290,339, filed Aug. 15, 1994, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to prosthetic feet and, more particularly,to a simply constructed, low-profile prosthetic foot having enhanceddynamic performance characteristics.

2. Description of the Related Art

In the prosthetics market, the conventional SACH foot has been the mostwidely prescribed artificial foot over the past 35 years. The SACH footgenerally includes a solid ankle and cushioned heel foot mounted to alimb along an approximate hinge axis taken through the ankle. The SACHfoot has been popular precisely for its simplicity, and thus economy,but includes certain drawbacks in terms of dynamic responsecharacteristics. Specifically, the low end SACH feet do not provide muchenergy storage and release, as do more sophisticated prosthetic feet.

Some patients undergo what is known in the art as a Symes amputation,where the foot is severed from the leg near the ankle region. Becausethe Symes patient's calf and shin function as the stump for prostheticpurposes, prosthetic devices utilized by the patient must either berelatively compact, so as to be attachable below the point ofamputation, or must be configured to accommodate the patient's shin andcalf while attached thereto or higher up on the wearer's leg. Prior artprostheses available to Symes patients typically include an artificialfoot bonded or bolted onto the bottom end of a socket worn on apatient's stump. These compact prosthetic feet can also attach below adownwardly depending pylon secured to a socket higher up on theamputee's leg. For such compact prostheses, it is difficult to providethe level of dynamic response approximating the original ankle and footdue to the lack of vertical space available. Some attempts at providingthe appropriate response characteristics of the original ankle and footin Symes foot prosthesis involve the use of rubber cushions, or bumpers,between a lower leg and the foot. Many of these require a pivotable boltattachment between the leg and the foot. Unfortunately, many of theserubber cushion devices have limited durability due to the difficulty inbonding the rubber portions to the solid leg or foot portions, or arerelatively complex, requiring several machined parts, which adds to thecost.

Consequently, there is a need for an inexpensive and durable Symes footprosthesis with improved performance characteristics.

SUMMARY OF THE INVENTION

In response to problems with the prior art, the present inventionprovides a simple, inexpensive prosthetic foot having a curvilinear footelement, an ankle element, and an ankle block of compressible materialpositioned between and connected to the foot element and ankle element.Preferably, the foot element has a length roughly equal to the length ofa human foot, while the ankle element is somewhat shorter. This footelement is constructed of a resilient material capable of flexing alongits length. The prosthetic foot further has an attachment memberconnected to the ankle element opposite the ankle block for coupling thefoot to a downwardly depending leg. In one preferred embodiment, thefoot element has a tapered thickness. Further, the foot elementcomprises uplifted heel and toe ends and an arch region therebetween.

In the preferred embodiments, the foot element and the ankle elementboth comprise plates. In addition, the ankle block preferably comprisesa monolithic element constructed of foam. Also, desirably, the ankleelement is also capable of flexing along its length.

In another form, the present invention provides a basic prosthetic foothaving enhanced performance characteristics generally comprising a lowerfoot plate, an upper ankle plate, and a monolithic foam ankle blockjoining the two plates. Both the foot plate and the ankle plate areconstructed of strong, flexible material, preferably a vinyl ester basedcompound. The foot plate is sized approximately equal to a human footbeing replaced, while the ankle plate has a similar width but has ashorter length than the foot plate. The ankle block has a length andwidth approximately equal to the ankle plate and is aligned therewith.Preferably, an attachment member couples to a stump or lower-limb pylonof the wearer via a bolt. During a walking stride, the combination ofthe resilient ankle block and flexible plates provides a smooth rolloverfrom a heel-strike to a toe-off position.

Desirably, the ankle block is constructed of a high density polyurethanefoam. During a walking stride, the majority of the compressive forcesimparted by the wearer is absorbed by the ankle block, with a smallportion being absorbed by the flexible plates themselves.

Further advantages and applications will become apparent to thoseskilled in the art from the following detailed description and thedrawings referenced herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first preferred prosthetic foot of thepresent invention within an outer foot cosmesis shown in phantom;

FIG. 2 is a perspective exploded view of the prosthetic foot of FIG. 1.

FIG. 3a is an elevational view of the prosthetic foot in a heel-strikeposition of a walking stride;

FIG. 3b is an elevational view of the prosthetic foot in a flat positionof a walking stride;

FIG. 3c is an elevational view of the prosthetic foot in a heel-offposition of a walking stride;

FIG. 3d is an elevational view of the prosthetic foot in a toe-offposition of a walking stride;

FIG. 4 is a perspective view of an alternative preferred embodiment of aprosthetic foot having features of the present invention, the outer footcosmesis being shown in phantom for illustrative purposes only;

FIG. 5 is a perspective exploded view of the prosthetic foot of FIG. 4;and

FIG. 6 is a side elevational view of the prosthetic foot of FIG. 4 moreclearly showing a foot plate having a tapered thickness along itslength.

FIG. 7 is a graph of load (F) vs. displacement (x) of a prosthetic footconstructed in accordance with FIGS. 4-6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now with reference to FIGS. 1 and 2, a first embodiment of a prostheticfoot 20 of the present invention is shown in assembled and explodedperspective views, respectively. The prosthetic foot 20 generallycomprises a lower foot plate 22, an upper, smaller ankle plate 24, and alayer or block of resilient material 26 connecting the foot plate to theankle plate. The foot plate 22 has a length and width roughly equal tothe approximate length and width of the particular wearer's amputatedfoot and is sized to fit within an outer flexible cosmesis 28, shown inphantom. The ankle plate 24 and resilient block 26 have approximatelythe same horizontal cross-sectional size. The ankle plate 24 andresilient block 26 are centered transversely with respect to and aregenerally positioned over the back half of the foot plate 22. The ankleblock 26 is sandwiched between the foot plate 22 and ankle plate 24, andis preferably bonded to both plates. The foot plate 22 may also have alower sole cushion 30 providing protection for the inner surfaces of thecosmesis 28 from the corners of the foot plate.

The prosthetic foot 20 is connected to a stump or lower leg pylon (notshown) of a wearer via an attachment member 32. The attachment member 32is adapted to be fastened to an upper surface of the ankle plate 24 andincludes a coupling knob 34 for mating with a coupling member on thepylon. In the illustrated embodiment, the attachment member 32 comprisesa base plate 36, having the upstanding coupling knob 34 formedintegrally therewith. The attachment member further may include a pairof upstanding location pins 48, which help transmit torsional forcesbetween the pylon and the foot prosthesis 20.

A central threaded bore 38 in the knob 34 receives a fastening bolt 40extending upwardly through an aperture 42 in the ankle plate 24. Theresilient block 26 is preferably formed with a cavity 44 in its uppersurface to receive the downwardly protruding bolt head 46. Of course,other attachment members can be attached via the upwardly directedfastening bolt 40, as will be readily apparent to those of skill in theart. The center of the bolt 40 defines an attachment axis 47 which isgenerally aligned with the vertical centerline of an imaginary ankle soas to more faithfully simulate the location at which forces aretransmitted between leg and foot. This centerline is positionedrearwardly from the longitudinal center of the ankle plate 24 and block26 and, preferably, approximately two-thirds of the way from the frontend of the ankle plate 24 and ankle block 26. Thus, there issubstantially more resilient material forward of the centerline 47, aswell as the attachment member 32, than to the rear.

Both the foot plate 22 and the ankle plate 24 are preferably constructedof fiberglass, which provides strength and flexibility. Alternatively,the plates 22 and 24 may be formed by a plurality of lamina embedded ina hardened, flexible polymer. In other arrangements the plates 22 and 24may be formed of other materials, such as carbon fibers, as may beapparent to one skilled in the art. The desirable properties of theplates 22, 24 are that they are relatively resilient so as to withstandcracking upon application of repeated bending stresses, yet havesufficient flexibility to enhance the performance characteristics feltby the wearer, in conjunction with the properties of the resilient ankleblock 26.

To more fully explain the improved performance characteristics of thepresent prosthetic foot 20, FIGS. 3a-3d show "snapshots" of a prostheticfoot in several positions of a walking stride. More particularly, FIG.3a shows a heel-strike position, FIG. 3b shows a generally flatposition, FIG. 3c shows a heel-off position, and FIG. 3d shows a toe-offposition. Throughout the various positions shown for a walking stride,the present prosthetic foot 20 provides a smooth and generally life-likeresponse to the wearer. During a walking stride, the ankle block 26transmits the forces imparted thereon by the foot plate 22 and ankleplate 24, and experiences a gradual rollover, or migration of thecompressed region, from rear to front.

With specific reference to FIG. 3a, a first position of a walking stridegenerally entails a heel strike, wherein the wearer transfers all of hisor her weight to the heel of the leading foot. In this case, a rearportion 50 of the foot plate 22 comes in contact with a ground surface52, albeit through the sole cushion 30 and cosmesis 28. The flexiblenature of the foot plate 22 allows it to bend slightly in the rearportion 50, but most of the compressive stresses from the weight of thewearer through the prosthetic foot 20 to the foot plate 22 are absorbedby a rear region 54 of the ankle block 26. Further, a slight amount ofbending may occur in a rear region 56 of the ankle plate 24, althoughthis bending is limited by the short lever arm between the axis ofattachment 47 and effective center of application of resisting force bythe walking surface on the foot 20. Additionally, the ankle block 26reinforces all but a small portion of the rear portion 50 of the footportion against bending. A front portion 58 of the ankle block 26experiences a stretching, or tension, due to the attachment along theentire lower edge of the ankle block with the foot plate 22.

Next, in FIG. 3b, the wearer reaches a generally flat-footed position,whereby the foot plate 22 contacts the ground 52 along substantially itsentire length, again through the sole cushion 30 and cosmesis 28. Inthis position the weight of the wearer is directed substantiallydownwardly, so that the compression along the length of the ankle block26 is only slightly greater in the rear portion 54 due to the off-centerapplication of force. Although this view freezes the compressive stressdistribution as such, in reality the weight of the wearer is continuallyshifting from behind the centerline 47 of the attachment member 32 toforward thereof. Thus, as the wearer continues through the stride, thecompression of the ankle block 26 travels from the rear portion 54toward the front portion 58. This migration of the compressed region canbe termed "rollover."

In a next snapshot of the walking stride, FIG. 3c shows the prostheticfoot 20 in a "heel-off" position. This is the instant when the wearer ispushing off using ball 60 and toe 62 regions of the foot. Thus, a largecompressive force is generated in the front region 58 of the ankle block26, causing the rear region 54 to experience a large amount ofseparation or tension. The front tip 64 of the foot plate 22 may bendsubstantially to absorb some of the compressive stresses. Likewise, thefront tip 66 of the ankle plate 24 may bend somewhat at this point. Itis important to note that although the ankle block 26 absorbs a majorityof the compression generated by the wearer, the foot plate 64 and ankleplate 66 are designed to work in conjunction with the resilient ankleblock and provide enhanced dynamic performance. Further, the flexing ofthe foot plate 64 and ankle plate 66 relieves some of the extreme sheerstresses applied to the interfaces between the ankle block 26 andplates, thus increasing the life of the bonds formed therebetween.

In FIG. 3d, a final position of the walking stride is shown, wherein theprosthetic foot 20 remains in contact with the ground 52, but some ofthe weight of the wearer is being transferred to the opposite foot,which has now moved forward. In this position, there is less bending ofthe front tip 64 of the foot plate 22 and less compression of the frontportion 58 of the ankle block 26. Likewise, the front tip 66 of theankle plate 24 may flex a slight amount, depending on the material andthickness utilized. The region of highest compression of the ankle block26 remains at the farthest forward region 58, but it is reduced from thecompression level of the heel-off position of FIG. 3c. Thus, the rearportion 54 of the ankle block 26 experiences a small amount of tensionor spreading.

Although the foot plate 22 is shown as substantially flat in theillustrations for the first preferred embodiment, it may alternativelybe constructed with a slight arch in the center region, with the toe andheel regions being slightly upwardly curved to simulate the naturalcurve of the sole of a human foot as illustrated in FIGS. 4-6. However,even with a flat foot plate 22, the foot 20 still performs substantiallybetter than other SACH feet.

Referring now in detail to FIGS. 4 and 5, an alternative preferredembodiment of a prosthetic foot 100 of the present invention isillustrated. The prosthetic foot 100, as shown in the assembled view ofFIG. 4, generally comprises a lower foot plate 110, an upper, smallerankle plate 112 and a resilient ankle block 114. The resilient ankleblock 114 is located intermediate the ankle plate 112 and the foot plate110. The foot plate 110 has a length and width roughly equal to theapproximate length and width of the particular wearer's amputated footand is sized to fit within the outer flexible cosmesis 28, shown inphantom. The ankle plate 112 and ankle block 114 are centeredtransversely with respect to and are generally positioned over the backportion of the foot plate 110. The ankle plate 112 and ankle block 114extend substantially more forwardly of the attachment axis 47 thanrearwardly.

The ankle block 114 is sandwiched between the foot plate 110 and theankle plate 112, as shown, and is preferably bonded to both plates. Alimit strap 116 further secures the foot plate 110, resilient ankleblock 114 and ankle plate 112. An attachment plate 118 is positionedover the limit strap 116 and is generally aligned with the rear end ofthe ankle plate 112. From FIG. 5, it can be seen that the attachmentplate 118 preferably includes a cutaway portion 120 to accommodate thethickness of the limit strap 116.

The prosthetic foot 100 is attached to a socket or lower leg pylon via abolt (not shown) which extends through a corresponding hole 122 in thefoot plate 110 and coaligned holes 124, 128, 130 formed in the ankleblock 114, the ankle plate 112 and the attachment plate 118,respectively. A stainless steel washer 126 is received in a recess 132formed on the top of the ankle block 114 in order to provide a flushinterface between the block 114 and the ankle plate 112. Otherattachment means, as may be apparent to those of skill in the art, mayalternately be utilized with the prosthetic foot of the presentinvention.

As illustrated in FIG. 6, the foot plate 110 is preferably ofcurvilinear shape. The thickness t along its length is tapered, and thetapered profile corresponds approximately to the weight of the amputee.That is, for a heavier amputee, the thicknesses along the length wouldbe greater than for a lighter weight amputee. Generally, the weightgroups may be classified as light, medium, or heavy.

Table I below presents preferred groupings, as module sizes C/D/E, ofcosmesis sizes corresponding to a male "A" width shoe last. The sizesare presented by length L, width B at the forefoot and width H at theheel of the cosmesis.

                  TABLE I                                                         ______________________________________                                        Cosmesis Sizes for Male "A" Width Shoe Last                                                           WIDTH B  WIDTH H                                      MODULE   LENGTH L (cm)  (cm)     (cm)                                         ______________________________________                                        C        22             2.88     2.19                                                                                    2.25                                                                          2.31                               D                                          2.44                                                                          2.50                                                                          2.56                               E                                          2.69                                                                          2.75                                            30                            2.81                               ______________________________________                                    

Table II below presents preferred module sizes for various weight groupsof amputees.

                  TABLE II                                                        ______________________________________                                        Modules vs. Weight Groups                                                            WEIGHT GROUP                                                           MODULE   LIGHT        MEDIUM   HEAVY                                          ______________________________________                                        C        CL           CM       --                                             D                  DL                   DH                                    E                  --         EM                                                                                      EH                                    ______________________________________                                    

Table III below presents preferred taper thicknesses (t) for an averageor "DM" size foot plate 110, taken at positions spaced by distance x=1inch (2.54 cm).

                  TABLE III                                                       ______________________________________                                        Taper Thickness t for DM Foot Plate                                           POSITION (x = 2.54 cm)                                                                         THICKNESS t (cm)                                             ______________________________________                                        a                0.16                                                         b                                              0.16                           c                                              0.32                           d                                              0.52                           e                                              0.69                           f                                              0.78                           g                                              0.71                           h                                              0.60                           i                                              0.48                           j                                              0.28                           ______________________________________                                    

The foot plate 110 has a heel end 134, toward the left in FIG. 6, isconcave-upward or slightly uplifted from a horizontal plane P₁tangential to the heel end 134 of the foot plate 110. Similarly, a toeend 136, to the right of FIG. 6, is concave upward or somewhat upliftedfrom a horizontal plane P₂ tangential to the front portion of the footplate 110. An arch section 138 is formed between the heel and toe endsand is preferably concave-downward, as shown.

It is understood that within the cosmesis 28 (FIG. 4), the tangent planeP₁ of the heel end 134 is slightly raised a distance y relative to thetangent plane P₂ of the toe end 136, as shown. The DM-sized foot plateof Table III, for example, has y=0.5 inches (1.27 cm). The foot plate110 is preferably 0.25 inches (0.63 cm) from the bottom or sole of thecosmesis 28. The cosmesis 28 may be insert molded using an anatomicallysculpted foot shape, with details and sizing based on a master patternand/or digitized data representing typical foot sizes.

An intermediate region 138 comprising the arch portion of the foot plate110 has the greatest thickness of the foot plate 110. The curvature ofthe arch region 138 is defined by the cosmesis or shoe sole profile, andgenerally corresponds to selected ranges of human foot lengths.

The ankle plate 112 is preferably shorter in length than the foot plate110 and has a thickness also defined by the weight group of the wearer.The ankle plate 112 is also preferably formed of a flexible material sothat flexing of the foot plate 110 and ankle plate 112 tends to relieveextreme sheer stresses applied to the interfaces between the ankle block114 and the plates 110, 112. The preferred material for the ankle plate24,112 and the foot plate 22,110 is a vinyl ester based sheet moldingcompound, such as Quantum #QC-8800, available from Quantum Composites ofMidland, Mich.

The ankle block 114 is generally sized such that its upper surface 140is planar and corresponds to the length and width of the ankle plate112. A lower surface 142 of the ankle block 114 is longer than its uppersurface 140 and generally corresponds to the contour and size of thearch region 138 of the foot plate 110. A downwardly sloping frontsection 144 of the ankle block 114 forms a face 146 connecting the upperand lower surfaces 140, 142 of the ankle block 114. The face 146 formsan angle θ of approximately 15° to the vertical or to the attachmentaxis 47, extending downwardly from the ankle plate 112 to the foot plate110. Alternatively, other angles θ ranging from about 5° to about 45°may be used to achieve the benefits taught herein. The particular shapeof the ankle block 114 causes it to distribute and transfer compressionstress uniformly. The shorter length of the ankle plate 112 and thesloping front section 144 of the ankle block 114 tend to reduce shearstresses occurring near the front tip of the ankle plate 112, whichcould otherwise cause undesirable delamination of the foot 100.

For the example given in Table III for a DM-sized foot plate 110, thelength of the plate 110 is approximately 9.05 inches (22.81 cm) and itswidth is about 2.0 inches (5.04 cm). The hole 122 is centered about 2.31inches (5.82 cm) from the rear edge (position a), and the diameter ispreferably 0.75 inches (1.89 cm). The corresponding ankle block 114 forthis example has a width of about 1.85 inches (4.66 cm), and the lengthof a top surface 140 is about 4.75 inches (11.97 cm). The recess 132 ispreferably 1 inch (2.54 cm) in diameter, and the hole 124 is 0.63 inches(1.59 cm) in diameter. The hole 124 and recess 132 are desirablycentered 1.31 inches (3.30 cm) from the rear edge of the ankle block114.

In the present example, the block 114 has a preferred maximum thickness,at its front, of about 1.30 inches (3.28 cm), and its thickness tapersto a minimum of about 0.83 inches (2.09 cm). The rear of the block 114is preferably about 1.06 inches (2.67 cm), which is less than the frontof the block 114 due to the raised heel end 134 of the foot plate 110.The corresponding ankle plate 112 in the present example is preferablyabout 0.22 inches (0.55 cm) thick, and approximately 4.75×1.85 inches(11.97×4.66 cm). The hole 128 is preferably about 0.41 inches (1.03 cm)in diameter.

The attachment plate 118 is sized to about 2.62×1.85 inches (6.60×4.66cm), and has a thickness of about 0.12 inches (0.30 cm) at the front andabout 0.06 inches (0.15 cm) at the rear to accommodate the strap 116.The cutaway portion 120 extends about 0.80 inches (2.02 cm) from therear end of the plate 118. The plate hole 130 is also about 0.41 inches(1.03 cm) in diameter.

The washer 126 is preferably about 0.125 inches (0.32 cm) thick and hasan outer diameter of about 0.938 inches (2.36 cm) and an inner diameterof 0.406 inches (1.02 cm). The limit strap 116 is preferably about 0.75inches (1.89 cm) wide and forms an inner circumference of about 6.40inches (16.13 cm) in the present example for a DM-sized foot plate 110.The strap 116 is desirably about 0.06 inches (0.15 cm) thick.

A preferred material for the ankle block 26, 114 is expandedpolyurethane such as Cellular Vulkolka® Pur-Cell #15-50, with a densityapproximately 500 kg/m³, as available from Pleiger Plastics Company ofWashington, Pa. Alternatively, the ankle block may be molded orfabricated from a wide variety of other resilient materials, as desired,such as natural or synthetic rubber, plastics, honeycomb structures orother materials. Cellular foam, however, provides a desirableviscoelastic springiness for a more natural feeling stride without thedrawback of limited compression associated with solid elastomericmaterials. Furthermore, the cellular nature of the block 26, 114 makesit lighter than solid elastomers. Foam densities between about 150 and1500 kg/m³ may be used to obtain the benefits of the invention taughtherein.

The ankle block 26, 114 may be provided in varying heights orthicknesses, as desired, but is most effective with a thickness ofbetween about 1 and 3 inches (2.54 and 7.56 cm). The ankle block thusprovides a relatively stiff, yet flexible ankle region which can becustomized for various wearers. Heavier wearers may require a denserresilient material for the ankle block, while lighter wearers mayrequire a less dense material or less thickness.

The limit strap 116 serves to contain or control the separation ordelamination of the rear portions of the foot plate 110, ankle block 114and ankle plate 112 during the heel-off portion of the amputee's stride,when the rear of the foot 100 undergoes maximum tension. The strap 116preferably forms a snug fit around this sandwiched assembly. The strap116 desirably has an overlap 148 of approximately 1 inch (2.54 cm) whichis sewn using a cross-stitch of heavy nylon thread. The strap 116 may beformed of any durable material; although, woven nylon is preferred.Although the strap 116 is shown with the overlapped portion 148 beneaththe attachment plate 118, it is understood that the overlap 148 may bepositioned otherwise, such as on the outside of the foot contactingneither the attachment plate 118 or the foot plate 110.

The attachment plate 118 is preferably shorter in length than the ankleplate 112, as shown, and is connected to the top surface of the ankleplate 112 at its rearward portion. The top surface of the attachmentplate 118 forms a mating surface for receiving a socket or the pylon ofa prosthetic lower limb. A preferred material for the attachment plate118 is a urethane elastomer; although, any similar durable material maybe utilized, as desired.

The thicknesses of the foot plate 110 and ankle plate 112 may becustomized for the wearer according to his/her foot size as well as theapproximate weight group of the wearer. Likewise, the material choiceand size for the ankle block 114, limit strap 116 and attachment plate118 may be varied according to the wearer's foot size and weight.

The preferred embodiment of FIGS. 4-6 provides a particularly smooth andlife-like response during normal walking or running activities. Theuniquely curved and sloped ankle block 114 transmits the forces impartedthereon by the foot plate 110 and ankle plate 112 such that the rolloveror migration of the compressed region is even more gradual and naturalas felt by the amputee. During heel strike the weight of the amputee isinitially transmitted to the heel of the leading foot, and thecompressive stresses are absorbed by a rear region of the ankle block114. As the amputee continues through his stride, the compression of theankle block 114 travels smoothly and continuously toward the frontportion, giving the foot a natural feel.

FIG. 7 is a graph of load (F) vs. displacement (x) of a prosthetic footconstructed in accordance with FIGS. 4-6. The test specimen wassubjected to various toe-loads applied with the foot prosthesis mountedat an angle ∫o of 20 degrees from vertical, as illustrated in theaccompanying schematic drawing.

Although not illustrated, the prosthetic foot of the present inventionalso provides enhanced performance for the wearer in inversion oreversion. Prior SACH feet were often relegated to pivoting about ahorizontal axis through the ankle and had relatively little flexibilityfrom side to side. The present invention allows the wearer to walktransversely upon sloped surfaces, for example, with the foot plategenerally conforming to the terrain while the ankle plate remainsrelatively horizontal due to the sideways compression of the ankleblock. Again, as the wearer lifts his or her foot, the ankle blockresumes its original shape, thus helping the wearer as energy is storedand then released.

It can now be appreciated that the "feel" of the present prosthetic footis greatly enhanced by the cooperation between the foot plate, ankleplate, and ankle block. As the wearer continues through the walkingstride, the dynamic response from the prosthetic foot is smooth as theankle block compresses in different regions. Further, the flexing of theankle and foot plates assists in smoothly transmitting the various bumpsand jars found in uneven walking surfaces.

The embodiments illustrated and described above are provided merely asexamples of certain preferred embodiments of the present invention.Other changes and modifications can be made from the embodimentspresented herein by those skilled in the art without departure from thespirit and scope of the invention, as defined by the appended claims.

What is claimed is:
 1. A prosthetic foot for providing resilientkinematic support to an amputee, said prosthetic foot comprising:a lowerfoot plate element having a length from toe to heel roughly equal tothat of a natural human foot being replaced, said foot plate elementbeing formed of a monolithic composite material having an area moment ofinertia about a first axis that is substantially smaller than he areamoment of inertia about a second axis perpendicular to said first axissuch that said foot plate element is capable of flexing along its lengthin a fore-and-aft direction, but not substantially in a side-to-sidedirection, said foot plate element defining toe and heel portions ofsaid prosthetic foot; an upper ankle plate element having a lengthshorter than said foot plate element and being separately formed of amonolithic composite material having an area moment of inertia about afirst axis that is substantially smaller than the area moment of inertiaabout a second axis perpendicular to said first axis such that saidankle plate element is capable of flexing along its length in afore-and-aft direction, but not substantially in a side-to-sidedirection; said ankle plate element and said foot elate element beingspaced apart from one another alone their entire length, and an ankleblock comprising a compressible material having a thickness of betweenabout 0.83 inches and about 1.30 inches, said ankle block beingpositioned between said ankle plate element and said foot plate element;and an attachment member secured to said ankle plate element adapted toattach said prosthetic foot to a pylon or socket, said attachment memberdefining an attachment axis located posteriorly along a longitudinalcenter line at a point approximately two-thirds of the distance rearwardalong the length of said ankle plate element; said foot plate element,said ankle plate element and said ankle block cooperating such that assaid amputee walks on said foot, compression stress migratessubstantially uniformly through said ankle block such that substantiallysmooth rollover of said foot prosthesis is achieved.
 2. The prostheticfoot of claim 1, wherein said ankle block extends roughly said length ofsaid ankle plate element.
 3. The prosthetic foot of claim 1, whereinsaid foot plate element comprises a resilient plate formed from aplurality of laminae embedded in a hardened flexible polymer material.4. The prosthetic foot of claim 3, wherein said ankle plate elementcomprises a resilient plate formed from a plurality of laminae embeddedin a hardened flexible polymer material.
 5. The prosthetic foot of claim1, wherein said ankle block comprises a monolithic block formed of arelatively compliant compressible material.
 6. The prosthetic foot ofclaim 5, wherein said ankle block is formed of a polyurethane material.7. The prosthetic foot of claim 6, wherein said ankle block is formed ofa cellular polyurethane foam having a density of between about 25-35lbs/ft³.
 8. The prosthetic foot of claim 1, wherein said ankle blockcomprises a monolithic block formed of a natural or synthetic rubber. 9.A prosthetic foot for replacing a natural human foot, said prostheticfoot comprising:a lower plate element having a length and width roughlyequal to that of said natural human foot being replaced and having topand bottom surfaces, said lower plate element being formed of amonolithic composite material capable of flexing substantially along itslength and having an area moment of inertia about a first axis that issubstantially smaller than the area moment of inertia about a secondaxis perpendicular to said first axis such that said lower plate elementis capable of flexing along its length in a first direction but notsubstantially in a second direction, said lower plate element comprisinga toe end, a heel end, and an intermediate region therebetween, saidlower plate element being tapered such that it decreases in thicknessfrom said intermediate region to said heel and toe ends so as to providedesired bending and energy storage characteristics; an upper plateelement having a length shorter than said lower plate element and havingtop and bottom surfaces, said upper plate element being formed of amonolithic composite material and having an area moment of inertia abouta first axis that is substantially smaller than the area moment ofinertia about a second as perpendicular to said first axis such thatsaid upper plate element is capable of flexing along its length in afirst direction, but not substantially in a second direction; aresilient ankle member composed of a compressible material sandwichedbetween said lower plate element and said upper plate element, saidankle member comprising a top surface and a bottom surface, the bottomsurface of said ankle member being matingly bonded to the top surface ofsaid lower plate element, the top surface of said ankle member beingmatingly bonded to the bottom surface of said upper plate element, suchthat said lower and upper plate elements and said ankle member arethereby maintained in intimate cooperative contact with one anotheralong their respective mating surfaces; and an attachment member securedto said upper plate element adapted to attach said prosthetic foot to apylon or other intermediate prosthetic member, said attachment memberdefining an attachment axis located along a longitudinal center line ofsaid prosthetic foot at a point such that more of said ankle member isdisposed forward of the attachment axis than is disposed rearward of theattachment axis.
 10. The prosthetic foot of claim 9, wherein saidposterior section of said foot plate comprises an raised heel.
 11. Theprosthetic foot of claim 9, wherein said ankle block comprises amonolithic block formed of a polyurethane material.
 12. The prostheticfoot of claim 9, wherein said ankle plate is generally parallel to saidfoot plate.
 13. A prosthetic foot for attaching to a socket, pylon orintermediate prosthetic device used to support a lower-limb amputee,comprising:a foot plate element, including posterior, medial andanterior sections, having a length approximately equal to the length ofa natural human foot, said foot plate element comprising a resilientmaterial capable of flexing along its length, said foot plate elementhaving a tapered thickness along its length, such that said thicknessincreases from said posterior section to said medial section anddecreases from said medial section to said anterior section; an ankleplate element having a length substantially shorter than said foot plateelement; and an ankle block comprising a relatively soft, compressiblematerial sandwiched between said ankle plate element and said foot plateelement, said ankle block providing substantially the sole means ofsupport and connection between said foot plate and said ankle plate andsaid ankle block being sized and positioned such that at least a portionof said posterior section of said foot plate element extends beyond saidankle block; whereby said foot plate and said ankle block flex in acooperative manner to provide substantially smooth and continuousrollover transition from heel-strike to heel-off.
 14. The prostheticfoot of claim 13, wherein said posterior section of said foot plateelement includes an raised heel.
 15. The prosthetic foot of claim 13,wherein said ankle block comprises a monolithic block formed of apolyurethane material.
 16. The prosthetic foot of claim 13, wherein saidankle plate element is generally parallel to said foot plate element.17. The prosthetic foot of claim 13, further comprising an attachmentmember secured to said ankle plate element adapted to attach saidprosthetic foot to a pylon or other intermediate prosthetic member, saidattachment member defining an attachment axis located posteriorly alonga longitudinal center line at a point approximately two-thirds of thedistance rearward along the length of said ankle plate element.
 18. Theprosthetic foot of claim 17, wherein said posterior section of saidlower foot plate element is substantially raised from a supportingground surface when said attachment axis is oriented substantiallyperpendicular to said ground surface.